For internal combustion engines, it is desired to enhance thermal efficiency; in other words, fuel economy. In order to enhance thermal efficiency, internal combustion engines including the following are known: a forced induction device, an exhaust gas recirculation (EGR) system for circulating exhaust gas in a gas intake passage, and a valve timing variable mechanism which opens and closes intake valves of two or more intake ports at different timings.
There are also internal combustion engines combining a forced induction device, an EGR system, and a valve timing variable mechanism. Such internal combustion engines perform control to first introduce EGR gas into a combustion chamber and then fresh gas using the forced induction device (refer to, for example, International Publication No. WO 2011/125208).
An internal combustion engine may combine a first intake port having a strong swirl generating power, a second intake port having a weak swirl generating power, and a valve timing variable mechanism. Such an internal combustion engine is controlled such that when a load is low, the first intake port alone is used to generate a strong swirl in a combustion chamber, whereas when a load is high, the first and the second intake ports are both used to enhance filling efficiency of the combustion chamber with intake gas (for example, refer to JP H04-179825A).
In the internal combustion engine which opens and closes intake valves at different timings, the amount of gas introduced from the valve which is later opened and closed increases. In internal combustion engines, the temperature in a cylinder rises along with an increase in the amount of gas introduced around bottom dead center. A combustion rate, which significantly affects thermal efficiency, highly depends on the temperature. Accordingly, it is necessary to optimally control the temperature in the cylinder in order to maximize thermal efficiency. However, neither International Publication No. WO 2011/125208 nor JP H04-179825A perform such controls.
An object of the present disclosure is to enhance the thermal efficiency of an internal combustion engine by controlling the temperature in a cylinder by controlling the amount of intake gas.